Add Line::flipped, Line::midpoint

CHANGELOG.md

@@ -23,6 +23,7 @@ This release has an [MSRV][] of 1.65.
 - Add `Arc::flipped`. ([#367] by [@waywardmonkeys])
 - Add `CircleSegment::inner_arc` and `CircleSegment::outer_arc` ([#368] by [@waywardmonkeys])
 - Add `Rect::is_zero_area` and `Size::is_zero_area` and deprecate their `is_empty` methods. ([#370] by [@waywardmonkeys])
+- Add `Line::flipped` and `Line::midpoint`. ([#375] by [@waywardmonkeys])
 
 ### Changed
 
@@ -61,6 +62,7 @@ Note: A changelog was not kept for or before this release
 [#367]: https://github.com/linebender/kurbo/pull/367
 [#368]: https://github.com/linebender/kurbo/pull/368
 [#370]: https://github.com/linebender/kurbo/pull/370
+[#375]: https://github.com/linebender/kurbo/pull/375
 
 [Unreleased]: https://github.com/linebender/kurbo/compare/v0.11.0...HEAD
 [0.11.0]: https://github.com/linebender/kurbo/releases/tag/v0.11.0

src/line.rs

@@ -34,12 +34,32 @@ impl Line {
         }
     }
 
+    /// Return a copy of this `Line` in the opposite direction.
+    #[must_use]
+    #[inline]
+    pub fn flipped(&self) -> Line {
+        Self {
+            p0: self.p1,
+            p1: self.p0,
+        }
+    }
+
     /// The length of the line.
     #[inline]
     pub fn length(self) -> f64 {
         self.arclen(DEFAULT_ACCURACY)
     }
 
+    /// The midpoint of the line.
+    ///
+    /// This is the same as calling [`Point::midpoint`] with
+    /// the endpoints of this line.
+    #[must_use]
+    #[inline]
+    pub fn midpoint(&self) -> Point {
+        self.p0.midpoint(self.p1)
+    }
+
     /// Computes the point where two lines, if extended to infinity, would cross.
     pub fn crossing_point(self, other: Line) -> Option<Point> {
         let ab = self.p1 - self.p0;
@@ -302,6 +322,18 @@ impl Iterator for LinePathIter {
 mod tests {
     use crate::{Line, ParamCurveArclen, Point};
 
+    #[test]
+    fn line_flipped() {
+        let l = Line::new((0.0, 0.0), (1.0, 1.0));
+        let f = l.flipped();
+
+        assert_eq!(l.p0, f.p1);
+        assert_eq!(l.p1, f.p0);
+
+        // Flipping it again should result in the original line
+        assert_eq!(l, f.flipped());
+    }
+
     #[test]
     fn line_arclen() {
         let l = Line::new((0.0, 0.0), (1.0, 1.0));
@@ -313,6 +345,12 @@ mod tests {
         assert!((t - 1.0 / 3.0).abs() < epsilon);
     }
 
+    #[test]
+    fn line_midpoint() {
+        let l = Line::new((0.0, 0.0), (2.0, 4.0));
+        assert_eq!(l.midpoint(), Point::new(1.0, 2.0));
+    }
+
     #[test]
     fn line_is_finite() {
         assert!((Line {